Aircraft jet engines possess in a known way one or more compressor stages, a combustion chamber and also one or more turbine stages. In the turbine stages, the hot combustion gases coming from the combustion chamber discharge part of their thermal and mechanical energy which is utilized in order to drive the compressor stages. Jet engines of commercial aircraft nowadays have most predominantly what is known as a turbofan which is arranged upstream of the compressor stages and, as a rule, has a considerably larger diameter than the compressor stages. The turbofan is likewise driven by the turbine stages and allows a considerable part of the air flowing overall through the engine to flow as what is known as a secondary airstream past the compressor stages, the combustion chamber and the turbine stages. By means of such a secondary stream, the efficiency of an engine can be increased considerably, and, moreover, care can also be taken to ensure an improved noise insulation of the engine.
A contamination of an aircraft jet engine may lead to a reduction in efficiency, thus resulting in an increased fuel consumption and consequently in increased environmental pollution. The contamination may be caused, for example, by insects, dust, salt mist or other environmental impurities. Parts of the engine may be contaminated by combustion residues from the combustion chamber. These impurities form a coating on those parts of an aircraft engine through which air flows, and are detrimental to the surface quality. The thermodynamic efficiency of the engine is consequently impaired. In this case, in particular, mention must be made of the blades in the compressor stages, the contamination of which blades has a considerable influence on the efficiency of the overall engine.
To eliminate impurities, it is known to clean an engine by means of a cleaning liquid, as a rule hot water. WO 2005/120953 discloses an arrangement in which a plurality of cleaning nozzles are arranged upstream of the turbofan or of the compressor stages. The cleaning liquid is then sprayed into the engine. The engine may in this case rotate in what is known as the dry cranking mode, that is to say rotate the blades of the engine, without kerosene being burnt in the combustion chamber. By means of the cleaning liquid introduced into the engine, dirt is to be washed off from the surfaces of the engine components in this way.
Alternatively to the use of water as a cleaning medium, it is known to use coal dust. The coal dust is in this case introduced through nozzles into the engine, in the same way as water, and strips away impurities from surfaces by virtue of abrasive effects. However, the surface of the engine parts is also attacked by the coal dust, and therefore a cleaning medium such as coal dust is not suitable for the regular cleaning of aircraft engines. Moreover, in cleaning with coal dust, undesirable residues of the cleaning material remain behind in the engine.